Compact and efficient spectrometers are essential for biological and environmental sensing applications in which optical signals of interest are usually very weak and portability is highly desired. Due to their wavelength selectivity, gratings have been used in conventional spectrometers. For example, multiple wavelength channels of a spatially coherent input source can be separated by rotating a grating. For a spatially incoherent source, adding a narrow slit and lens (i.e., to make a collimated beam) in front of the grating is required to avoid the ambiguity between the incident wavelength and the incident angle. However, since most of the input power is blocked by the slit and some space is needed to add the lens, conventional spectrometers are inefficient and bulky.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.